A wide variety of disposable absorbent structures designed for the absorption of bodily fluids, such as urine and menses, are known. Such products generally comprise some sort of fluid-permeable topsheet material, an absorbent core, and a fluid-impermeable backsheet material. The bulk of such products is often the absorbent core component, such that a typical disposable diaper having an absorbent core consisting primarily of wood pulp fibers consists of about 80% biodegradable materials. However, the remaining components generally comprise materials which are typically considered to be non- or marginally- biodegradable. For example, topsheet and backsheet materials are often prepared from polypropylene or polyethylene.
The biodegradability of disposable absorbent products has recently been emphasized. Although these disposable products typically largely comprise materials that would be expected to ultimately biodegrade, and although such products contribute only a very small percentage of the total solid waste materials generated by consumers each year, there is nevertheless a currently perceived need to devise such disposable products from materials that biodegrade relatively quickly, thereby lessening their bulk. There is a particular need to replace polyethylene backsheets with liquid impervious, biodegradable films since the backsheet is typically the largest non-biodegradable component of an absorbent article. To avoid a buildup of man-made materials in the soil, it is desirable that such materials be fully biodegradable, i.e., biodegradation is complete to carbon dioxide, water, biomass, minerals, and optionally methane. It is further desirable that biodegradation occur as rapidly as possible, in order to avoid the accumulation of man-made materials in the soil. It is also desirable that these biodegradable materials be compostable.
Microbial degradation of "natural" polymers such as starch, cellulose, and lignin typically involves an initial hydrolysis of the polymer by extracellular enzymes (enzymatic hydrolysis). The resultant monomers or low molecular weight oligomers can be internalized and subsequently metabolized by a variety of intracellular enzymes.
Various synthetic polymers for use in disposable absorbent articles have been described as biodegradable. For example, International Publication No. WO 92109654 describes aliphatic-aromatic copolyesters derived from dicarboxylic acids or derivatives thereof and aliphatic diols, and binary blends of cellulose esters with aliphatic-aromatic copolyesters. Polymeric compositions comprising a destructurized starch component and a polymeric component consisting of a blend of hydroxyacid polymers and ethylene-vinyl alcohol or polyvinyl alcohol are disclosed in International Publication No. WO 90/10671. The preparation of polyesters based upon copolymerization of polyethylene terephthalate and non-aromatic diacids such as adipic and glutaric acids with sulfoisophthalic acid derivatives are described in U.S. Pat. No. 5,171,308 and the associated parent applications.
Although the above polymer materials may meet certain requirements for composting (e.g., facile physical fragmentation with ultimate loss of macroscopic structural integrity), the ability to completely biodegrade to carbon dioxide, water, biomass, minerals, and optionally methane within a period of time comparable to materials which are generally recognized as biodegradable and compostable, such as yard waste, has yet to be demonstrated. In particular, synthetic polymers such as aromatic-aliphatic copolyesters are not readily biodegradable because microbes have not yet evolved with the requisite extracellular enzymes to generate low molecular weight oligomers and/or monomers which can be metabolized. Therefore, there is a continuing need to enhance both the degree (i.e., the extent) and rate of biodegradation of such polymeric materials.
Toilet-flushable sanitary products containing binder resins that are degradable in toilet water upon the addition of water-soluble acids or bases to the toilet water have been disclosed. See, for example, U.S. Pat. No. 3,480,016 issued to Costanza et al., on Nov. 25, 1969 and U.S. Pat. No. 3,707,430 issued to Costanza et al., on Dec. 26, 1972. However, these patents do not describe the incorporation of the acids or bases into a polymer film. Indeed, the incorporation of such water-soluble acids and bases is believed to be unsuitable for forming polymer films and, more particularly, polymeric films for use in absorbent products intended for applications involving human contact, such as diapers. This is because such water-soluble acids and bases are strong acids and bases. It is believed that the incorporation of such materials into film products would present problems in manufacturing such as equipment corrosion, safety concerns, and moisture sensitivity. It is also believed that the incorporation of such materials into a polymer may result in premature hydrolysis of the polymer composition due to the hygroscopic character of such materials combined with their inherent acidity or basicity. Thus, such a composition may not be sufficiently stable for its intended use. This may be a particular problem in applications where the composition is exposed to moisture for extended periods, such as may occur with the overnight wearing of diapers. Such products may not retain sufficient integrity to satisfy consumer needs. In addition, the presence of strong acids and bases in components of absorbent articles wherein contact with human skin may occur presents toxicity concerns.
Thus there remains a need for film-processable polymers which are suitable for use in disposable absorbent articles and which have enhanced biodegradability. It is therefore an object of the present invention to provide biodegradable polymers which have increased rates of biodegradability. Another object of the invention is to provide such polymers which are fully biodegradable to carbon dioxide, water, biomass, and minerals. An additional object is to provide such materials which are non-toxic to humans and which remain sufficiently stable during use. Another object is to provide polymer materials which are compostable. Additional objects include providing disposable absorbent articles having enhanced biodegradability.